1. Field of the Invention
The present invention relates to a holding sealing material, a method for producing a holding sealing material, and an exhaust gas purifying apparatus.
2. Discussion of the Background
Exhaust gases discharged from internal combustion engines such as diesel engines contain particulate matter (also referred to as PM) such as soot, and in recent years, the harm that the PM causes to the environment and the human body has become a problem. Exhaust gases also contain harmful gas components such as CO, HC and NOx, and the harm that these harmful gas components cause to the environment and the human body has become a further problem.
To solve such problems, there have been proposed various exhaust gas purifying apparatuses including an exhaust gas-treating body formed of a porous ceramic material such as silicon carbide or cordierite, a casing for housing the exhaust gas-treating body, and a holding sealing material formed of inorganic fibers disposed between the exhaust gas-treating body and the casing, as exhaust gas purifying apparatuses for collecting PM in exhaust gases and purifying harmful gas components. The holding sealing material is disposed mainly for the purpose of preventing damage in the exhaust gas-treating body caused by a contact with the casing covering the periphery of the exhaust gas-treating body due to vibrations and impact generated during driving of the vehicle, and preventing leakage of exhaust gases from between the exhaust gas-treating body and the casing.
The holding sealing material is a rectangular mat having short sides and long sides in a plan view. Commonly, a quadrangle depression is formed on a first short side and a protrusion engaging with the depression is formed on a second short side that is an opposite side of the first short side. The holding sealing material is mainly formed of inorganic fibers such as alumina fibers.
In production of the exhaust gas purifying apparatus, a holding sealing material in the shape mentioned above is wound around an exhaust gas-treating body, and canning is performed for housing the exhaust gas-treating body (hereinafter, also referred to as a wound body) with the holding sealing material wound therearound in a casing by any available method.
JP-A 2002-4848 discloses a holding sealing material having features mentioned below for preventing scattering of inorganic fibers from a holding sealing material during the canning. Namely, an organic or inorganic binder is loaded on a mat-like material formed of inorganic fibers. The density of inorganic fibers is adjusted so that the packing density after winding is set within a range of 0.1 to 0.6 g/cm3. When the mat-like material is divided in the thickness direction into three parts including an upper part, a center part, and a lower part, distribution of solids in the binder loaded on the mat-like substance is higher in the upper and lower parts than in the center part.
The contents of JP-A 2002-4848 are incorporated herein by reference in their entirety.